1. Technical Field
The present invention relates to a roll for charging a belt for an inkjet recording apparatus and an inkjet recording apparatus, and especially relates to a roll for charging a belt, in which the roll performs charging of the belt and eliminating of the charge of the belt that transports a recording medium, and the inkjet recording apparatus.
2. Related Art
Conventionally, in an inkjet recording apparatus, images are formed on a recording medium by ejecting an ink liquid while the medium is scanned with an inkjet head moving in a main scanning direction, and after completing one scanning line, the medium is transported a predetermined increment in the sub-scanning direction, and the medium is scanned in the main scanning direction again.
In the transportation of the recording medium, because it is necessary to transport the medium a predetermined distance with high accuracy, the recording medium is transported while the medium is electrostatically attracted to the surface of a transporting belt by charging the transporting belt. When residual electric charges exist on the transporting belt, the desired amount of electric charge is not obtained so that a stable attraction force cannot be obtained.
In order to obtain a stable attraction force at the surface of the transporting belt, a method of a paper transporting apparatus equipped with a charge eliminating brush for eliminating charges on an electrostatic attraction belt has been known.
A method to perform charge elimination using a charge eliminating apparatus such as a corotron, a scorotron, a charge eliminating brush, and a charge eliminating roll in an apparatus such as an electrostatic recording apparatus is known.
However, in a paper transporting apparatus using a charge eliminating brush, the charge eliminating capability decreases at a part of transporting belt corresponding to the position where the brush bristles are deformed or have fallen out and the apparatus cannot perform stable charging property. Further, there is a concern that the bristles that have fallen out attach to other mechanisms in the paper transporting apparatus and cause adverse effects, and there is a problem that the reliability of the apparatus is lowered, for example, due to a concern of deteriorated charging property caused by bristles attached to a charger and a concern of deterioration in image quality caused by the bristles attached to the recording medium or the inkjet head.
In the method using the above-described charge eliminating apparatus such as a corotron and a scorotron, there is a problem that the apparatus is difficult to make small because of the additional requirement to have a mechanism to generate voltage and its required space, and also as a result, the cost of the apparatus as a whole increases. Further, the conventional corotron and scorotron are easily affected by the generation of ozone, surface hydrophilization, and discharging deterioration, and so such an apparatus is not preferable from the aspect of space taken up by the apparatus and cost.
On the other hand, in the conventional conductive roll using a direct current, although it is necessary to keep stability of the paper attraction properties by means of DC charging for maintaining an electric field retention when a belt is charged, electric characteristics are deteriorated because of contamination at the surface of the belt due to ink (or processing solution) mist and ink stain. Further, uneven charging due to change of shape and generation of recesses occurs easily.
In contrast, a conductive roll which enables charging of the transporting belt with high reliability with the aim of avoiding charge elimination has been provided. The conductive roll is simultaneously used for charging using both alternating current and direct current, and an electric resistance is controlled by a single layer conductive roll. However, the property of paper attraction of a paper such as a paper containing moisture varies easily with changes in the electric resistance due to environmental variations, and while the transportation and the charging of the belt are controlled, the residual charges on the belt vary with the location, size, and type of paper, and a stable attraction force cannot be obtained.